#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

int jump(int x)
{
    if (x <= 2)
        return x;
    else
        return jump(x - 1) + jump(x - 2);
}
int main()
{
    int n = 0;
    scanf("%d", &n);
    printf("%d\n", jump(n));

    return 0;
}